During the past year we continued our research on developing primate brain that has been obtained from the New England Regional Primate Research Center. Among projects that were completed is a longitudinal study on synaptogenesis in the cerebral cortex of the macaque monkey. In addition, we also continued our investigation of the primate retinal photoreceptor mosaic in collaboration with Drs. K. Wikler and P. MacLeish, which is build on a novel cone-specific monoclonal antibody, 7G6 generated by our team. This antibody stains specifically sub-populations of cones in the fetal monkey retina (Wikler et al, 1997). We also made considerable progress in our research on one of our major goals, which is to determine when and how the circuitry of M and P streams in the primate visual system becomes coordinated from the periphery (retina) to the center (cortex). Now that we have establish that m and P ganglion cells in the embryonic macaque retina diverge into their respective subtypes independently and prior to the formation of synaptic contacts (Meissirel et al., 1997), we are investigating possible developmental mechanisms. For this purpose, we plan to manipulate the relative size of M and P streams by selectively reducing M and P neurons in the geniculate nucleus by timed X-irradiation in the embryo, as we did in the deletion of specific layers of the visual cortex (Algan and Rakic, 1997). Last year we published a longitudinal study of the cell-cycle parameters in the proliferative ventricular zone of fetal macaque monkeys. To our surprise, we found that cell-cycle duration in monkeys was as much as 5-times longer than those reported for the smaller rodent neocortex (Kornack and Rakic, 1988). However, we also found that substantially more successive cell divisions elapsed during neurogenesis in monkeys than in rodents. Moreover, cell division accelerated during neurogenesis for the enlarged cortical layers in monkeys, in contrast to the progressive slowing described in rodents. Thus, evolutionary modification of the duration and number of progenitor cell divisions underlies both the expansion and laminar elaboration of the primate neocortex. In the next year, we will continue our search for the regional patterns of expression of various transcription factors and signaling molecules in the developing primate cerebral cortex.